Technology in Action Technology in Focus: Under the Hood 1 2 Electrical Switches The system unit contains the CPU The CPU uses a large number of switches Two states: 1 or 0 (on or off) Binary language consists of two numbers: 1 or 0 These switches are used to Lock process data Early Computer Switches Vacuum tubes Allow or block the flow of electrical current Take up a large amount of space Generate heat and burn out frequently Impractical due to size and reliability issues 3 4 Transistors Transistors Electrical switches built of layers of silicon Early transistors were built in separate units as small metal rods Each rod was a small on/off switch Smaller and faster than vacuum tubes Produced less heat Integrated Circuits Made of semiconductor material, silicon Contain huge number of transistors, resistors, capacitors, and diodes Small size, only ¼ inch in diameter 5 6 1
Microprocessors Chip that contains CPU Intel 4004 First complete microprocessor on a single integrated circuit Built in 1971 Contained 2,300 transistors Current CPUs contain more than 500 million transistors Base 10 Number System Organized plan for representing a number Base 10 or decimal notation Uses 10 digits (0 9) System used to represent all of the numeric values we use each day 10 3 1,000s place 10 2 100s place 10 1 10s place 10 0 1s place 6 * 1,000 + 9 * 100 + 5 * 10 + 4 * 1 (6,000 + 900 + 50 + 4) = 6,954 7 8 Base 2 Number System Hexadecimal Notation: Base 16 Base 2 or binary Uses two digits (1,0) Computers use binary because each switch can be in one of two positions: on or off. 2 3 8s place 2 2 4s place 2 1 2s place 2 0 1s place 1 0 1 1 (8 + 0 + 2 + 1) = 11 9 Base 16 (0 9, A F) Character representation Base 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Base 16 0 1 2 3 4 5 6 7 8 9 A B C D E F Hex 1A43 = 6,723 in Base 10 16 3 4,096s place 16 2 256s place 16 1 16s place 16 0 1s place 1 A 4 3 1 * 4,096 + 10 * 256 + 4 * 16 + 3 * 1 4,096 + 2,560 + 64 + 3 6,723 10 ASCII EBCDIC and Unicode American Standard Code for Information Interchange Pronounced As-key Represents each letter or character as an 8-bit (or 1-byte) binary code. ASCII Code Represents This Symbol ASCII Code Represents This Symbol 01000001 A 01100001 a 01000010 B 01100010 b 01000011 C 01100011 c 01011010 Z 00100011 # 00100001! 00100100 $ 00100010 00100101 % 11 EBCDIC Used by older mainframe computers Unicode Uses 16 bits (2 bytes) Multilanguage support Currently assigns more than 96,000 unique character symbols 12 2
Decimal Numbers Floating-point standard established by IEEE 32-bit (4-byte) system First bit (sign bit) indicates positive or negative Next 8 bits indicate magnitude (hundreds, millions, etc.) Remaining 23 bits store number CPU Machine Cycle All CPUs must perform a series of similar steps: Fetch Decode Execute Store 13 14 System Clock Control Unit Moves CPU from one stage of the machine cycle to the next Acts as a metronome, keeping a steady beat or tick Ticks, known as the clock cycle, set the pace Pace, known as clock speed, is measured in hertz (Hz) Manages switches inside the CPU Remembers Sequence of processing stages How switches are set for each stage Uses beat of system clock to move switch to correct on or off setting for each stage 15 16 Stage 1: The Fetch Stage Cache Memory Data and program instructions stored in various areas of the computer Data moved from storage to RAM CPU accesses RAM and moves data into registers Cache memory Stores recent or frequently used instructions Faster to access than RAM 17 18 3
Stage 2: The Decode Stage The CPU s control unit decodes a program s instructions into commands Instruction set The collection of commands a CPU can interpret Written in assembly language for programmers. Assembly language is translated into machine language for the CPU Stage 3: The Execute Stage Arithmetic logic unit (ALU) performs Mathematical operations Addition Subtraction Multiplication Division Test comparisons (<, >, =) Logical OR, AND, and NOT operations 19 20 Stage 4: The Store Stage Results produced by the ALU in Stage 3 are stored in the registers Moore s Law The number of transistors on a processor doubles every 18 months The first 8086 chip had 29,000 transistors and ran at 5 MHz Today s Penryn chip for notebook computers has 820 million transistors and runs at 2.6 GHz 21 22 Pipelining Boosts CPU performance CPU works on more than one stage or instruction at a time Multiple Processing Multiple processors or computers work on a problem simultaneously Dual- or multicore: Multiple processors in one computer Parallel processing: Multiple computers working on one problem Problem must be able to be divided into a set of independent tasks 23 24 4
DNA Computers Use DNA molecules and special enzymes instead of silicon chips 330 trillion operations per second 100,000 times faster than current silicon-based computers No practical applications yet All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Printed in the United States of America. Copyright 2011 Pearson Education, Inc. Publishing as Prentice Hall 25 Technology in Focus 26 5